1. Field of the Invention
The present invention relates generally to a cooling system and a control method applicable to the cooling system for a water- (or, liquid-) cooled internal combustion engine and, more particularly, relates to cooling system and control method applicable to the cooling system therefor in which a water pump to circulate an engine coolant to the engine is driven by means of its associated motor.
2. Description of the Related Art
A first previously proposed cooling system for the water-cooled engine includes the water pump driven in proportion to a revolution speed of the engine so that the coolant (a cooling water) is circulated into a cylinder head and a cylinder block. However, in the first previously proposed cooling system described above, since a flow quantity of the coolant is proportional to the revolution speed of the engine, an excessive amount of the coolant is circulated unnecessarily, in, for example, a winter season, and an extra amount of the coolant is unnecessarily circulated during a high speed run of an automotive vehicle in which the first previously proposed cooling system is mounted. Therefore, the first previously proposed water-cooled engine cooling system using the water pump generates an extra heat radiation of the coolant so that a delay in an engine warm-up occurs and has a considerably large loss in power. Furthermore, since only the revolution speed of the engine determines the flow quantity of the coolant, a high-temperature control cannot be achieved. To reduce the power loss described above, a Japanese Patent Application First Publication No. 2000-045774 published on Feb. 15, 2000 exemplifies a second previously proposed cooling system. In the above-described second previously proposed cooling system, a conventional water pump is replaced with a motor-driven water pump and such a control that a difference in temperature of the coolant at an outlet of the engine coolant and at an inlet of the engine coolant indicates a predetermined difference value is executed.
In general, if the circulation quantity of water is varied by means of the water pump, the coolant (or a cooling water) indicates a laminar flow state or a turbulence state depending upon a flow quantity of the coolant which is circulated through a multiple number of tubes disposed within headers of a radiator. For example, if the flow velocity of the coolant within the tubes is reduced and is below a predetermined flow velocity, the coolant becomes a laminar-flow state. A cooling efficiency is reduced at the radiator so that the engine is not well cooled and an increase in a power of a radiator fan cannot be avoided. In addition, in a case where the flow velocity of the coolant within the tubes becomes increased to indicate the turbulence flow state in the tubes, a further increase in the flow velocity of the coolant cannot provide a cause of the increase in the cooling efficiency and, in turn, the power required to cool the engine is increased.
These problems are applied equally well to the second previously proposed cooling system. That is to say, in each of the previously proposed cooling systems, even if the water pump is driven by means of the motor and even if a control such that the difference in the coolant temperature between at the outlet of the engine coolant and at the inlet of the engine coolant indicates the predetermined temperature difference is executed, the flow velocity of the coolant within the tubes of the radiator cannot be yet controlled. Therefore, in a case where the coolant becomes laminar, the cooling efficiency at the radiator becomes reduced and the coolant is not sufficiently cooled. Thus, the increase in the power of the radiator fan is required. On the contrary, if the flow velocity of the coolant is increased and the coolant becomes turbulence flow state, the cooling efficiency to meet with the increase in a working efficiency of the motor-driven pump cannot be achieved even if a working rate of the motor-driven pump is increased.
Furthermore, an excessive work of the motor-driven pump can possibly provide a cause of an erosion in the tubes
It is, therefore, an object of the present invention to provide cooling system for a water-cooled internal combustion engine and a control method applicable to the cooling system therefor in which a pump power to circulate the coolant is suppressed, a wasteful work of the radiator fan is prevented from occurring, an extra heat radiation of the coolant is prevented from occurring to fasten an engine warm-up, and an improvement in a fuel consumption of the water-cooled engine can be achieved.
According to one aspect of the present invention, there is provided a cooling system for a water-cooled internal combustion engine, comprising: a heat exchanger to circulate a coolant flowing out from the water-cooled engine into tubes arranged in a space between headers thereof to cool the coolant; a pump driven independently of the water-cooled engine to circulate the coolant into the water-cooled engine and the heat exchanger; a temperature detector to detect a temperature of the coolant; and a controller that drivingly controls the pump on the basis of a detected value of the coolant temperature by the temperature detector in such a manner as to control the drive of the pump for the coolant to be circulated by a predetermined flow quantity, when the temperature of the coolant detected by the temperature detector indicates a value higher than a predetermined target temperature, the heat exchanger being arranged, at the predetermined flow quantity of the coolant, to cause a stream state of the coolant circulated within the tubes of the heat exchanger to fall within a predetermined range including at least one of a transition range between a laminar flow range and a turbulence flow range and a part of the turbulence flow range which is placed in vicinity to the transition range.
According to another aspect of the present invention, there is provided a cooling system for a water-cooled internal combustion engine, comprising: a heat exchanger to circulate a coolant flowing out from the water-cooled engine into tubes arranged in a space between headers thereof to cool the coolant; a pump driven independently of the water-cooled engine to circulate a coolant to the water-cooled engine and the heat exchanger; a temperature detector to detect a temperature of the coolant; and a controller that drivingly controls the pump on the basis of a detected value of the coolant temperature by the temperature detector in such a manner as to control the drive of the pump for the coolant to be circulated by a predetermined flow quantity, when the temperature of the coolant detected by the temperature detector indicates a value higher than a predetermined target temperature, the heat exchanger being arranged, at the predetermined flow quantity of the coolant, to cause Reynolds number of the coolant circulated within the tubes of the heat exchanger to fall in a range between 1800 and 6000.
According to a still another aspect of the present invention, there is provided a control method applicable to a control system for a water-cooled internal combustion engine, the control system comprising: control method applicable to a control system for a water-cooled internal combustion engine, the control system comprising: a heat exchanger to circulate a coolant flowing out from the water-cooled engine into tubes arranged in a space between headers thereof to cool the coolant; a pump driven independently of the water-cooled engine to circulate the coolant to the water-cooled engine and the heat exchanger; and a temperature detector to detect a temperature of the coolant, the control method comprising: determining whether the temperature of the coolant detected by the temperature detector indicates a value higher than a predetermined target temperature; drivingly controlling the pump on the basis of a detected value of the coolant temperature by the temperature detector in such a manner as to control the drive of the pump for the coolant to be circulated by a predetermined flow quantity, when determining that the temperature of the coolant detected by the temperature detector indicates a value higher than a predetermined target temperature, at the predetermined flow quantity of the coolant; and causing a stream state of the coolant circulated within the tubes of the heat exchanger to fall within a predetermined range including at least one of a transition range between a laminar flow range and a turbulence flow range and a part of the turbulence flow range which is placed in vicinity to the transition range.
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.